During the last glaciation the area was invaded by two distinct ice sheets. One, from the Irish Sea basin, pushed southwards across the Cheshire-Shropshire Plain and sent a lobe down the Vale of Stretton and onto the northern slopes of the Long Mynd. The other was nourished in the Plynlimon massif and advanced from the west. Directions of ice movement, inferred from the orientation of ice-moulded landforms, drumlins, striations and the distribution of erratics, are complex, but the broad valleys were the main avenues of advance. Drift generally occupies valleys and covers the lower hillslopes, while erratics and scattered patches of till are found at higher altitudes. At the glacial maximum all save perhaps the highest hill summits were ice-covered. The Stiperstones tors are unreliable indicators of an inglaciated enclave. Deglaciation was characterised by a gradual downwastage, retreat and stagnation of the margins of the ice. Complex systems of subglacial drainage channels were cut in the Vale of Strettoa, and on all the major hill masses up to 1,300ft. Kaure moraines deposited across the Onny valley at Lydham Heath and the Mule - Caebitra valley at Sarn, indicate pauses in the ice retreat. Kamiform topography is also a feature of the northern slopes of the Long Mynd and the Vale of Stretton. Several important changes in, the drainage pattern resulted from glaciation. The Mule and Camlad were diverted across pre-glacial watersheds through meltwater channels, while the Onny was diverted through an ice-breached col and meltwater channel at the southern end of the Long Mynd. Radiocarbon dating of shells in the drifts at Iron Bridge, and of other drifts on the margins of the Welsh massif, indicate that the last glaciation of southern Shropshire was of Main Wurm age.